This invention relates to magnetic tape drives, and more particularly to mechanisms for transporting tape across a read/write head in the drives. All tape transport mechanisms include a pair of tape reels. The magnetic tape extends from one of the tape reels across the read/write head and across a capstan to the other tape reel. In operation, the capstan moves the tape across the read/write head at some predetermined velocity. This movement may be either in a forward direction or a backward direction. The patricular direction is determined by command signals that are sent to the drive.
As the capstan changes its velocity from one direction to another, the tape reels also change their direction of movement. However, the capstan has a much lower inertia than that of the tape reels. Therefore, when the tape movement changes from a forward direction to a reverse direction for example, a difference in velocity occurs between the capstan and the tape reels. In order to prevent the tape from tearing due to this difference in velocity, a pair of vacuum columns typically are included in the tape transport mechanism. These vacuum columns are positioned on either side of the capstan between the tape reels.
One of the factors that determines how fast the tape may be accelerated from one direction to the other is the length of the vacuum columns. In general, the maximum allowable acceleration varies directly with the length of the vacuum columns. Another factor that determines how fast the tape movement may be changed is the force exerted on the tape by any roller bearings between the two vacuum columns. These rollers are typically included to shape the tape path. However, a sudden change in velocity of the tape over such a roller produces a tension in the tape; and as the change in tape velocity is increased this tension will eventually cause the tape to tear.
Despite these two limitations on tape transport mechanisms, there exists a demand in the computer industry for reading and writing data from magnetic tapes at higher and higher speeds. Therefore it is one object of the invention to provide an improved tape transport mechanism for a magnetic tape drive.
Another object of the invention is to provide a tape transport mechanism that includes a pair of vacuum columns having no direction changing roller lying therebetween.
Still another object of the invention is to provide a tape transport mechanism having a pair of vacuum columns of maximum length for a tape drive cabinet of a given size.